Method and apparatus for perforating a casing and producing hydrocarbons

Abstract

A perforating gun and one or more volume-receiving surge canisters can be actuated at a time delay after perforation for creating a dynamic underbalance condition to aid in directing debris out of the perforations and fractures and into the wellbore. A timer and triggering device actuate one or more canisters in parallel or series after a pre-determined time delay or delays which can be related to wellbore conditions following perforation. Use of propellant-type perforating gun further benefits from favorable propellant burn conditions for forming perforations and followed thereafter by a perforation-cleaning underbalance pressure conditions characterized by one or more of an increased rate of change depression of the pressure in the adjacent annulus, a greater magnitude of pressure depression and a longer duration of underbalance.

1. A method for creating a period of dynamic underbalance at a zone of interest in a wellbore comprising:
 positioning a perforation assembly in the wellbore at the zone of interest for creating an annulus between the assembly and the wellbore, the annulus containing fluid and having an initial hydrostatic pressure, the assembly having at least a propellant-type perforation gun and one or more surge canisters, the initial hydrostatic pressure encouraging maximal burn of propellant of the propellant-type perforation gun; 
 actuating the propellant-type perforating gun for igniting the propellant, creating an initial pressure event and forming perforations at the zone of interest and wherein dynamic pressure in the annulus at the zone of interest reaches a first initial elevated pressure; 
 delaying until the dynamic pressure diminishes from the first initial elevated pressure; 
 wherein the initial pressure event creates an interface reflection pressure wave traveling along the wellbore and wherein the delaying further comprises delaying until about the time the interface reflection pressure wave reaches the zone of interest: and then 
 opening at least one of the one or more surge canisters so as to receive a surge of the fluid therein for creating the period of dynamic underbalance. 
 
     
     
       2. The method of  claim 1  wherein the initial hydrostatic pressure is at an overbalanced condition. 
     
     
       3. The method of  claim 1 , wherein the initial hydrostatic pressure is at a balanced condition. 
     
     
       4. The method of  claim 1  wherein the delaying further comprises delaying until the initial pressure event is substantially complete. 
     
     
       5. The method of  claim 4  wherein the initial pressure event is substantially complete when the dynamic pressure approaches a second threshold pressure lower than the first initial elevated pressure. 
     
     
       6. The method of  claim 1  wherein the delaying is a pre-determined time delay. 
     
     
       7. The method of  claim 6  further comprising calculating the predetermined time delay wherein the opening at least one of the one or more surge canisters occurs when the dynamic pressure approaches a second threshold pressure lower than the first elevated pressure event. 
     
     
       8. The method of  claim 7  wherein the second threshold pressure is at or near the initial hydrostatic pressure. 
     
     
       9. The method of  claim 1  wherein the delaying is a pre-determined time delay further comprising calculating the pre-determined time delay for the interface reflection pressure wave to reach the zone of interest. 
     
     
       10. The method of  claim 1  wherein the interface pressure wave acts to depress the dynamic pressure and wherein the delaying further comprises delaying until after the dynamic pressure is depressed by the interface reflection pressure wave. 
     
     
       11. The method of  claim 1  further comprising:
 measuring the dynamic pressure; and wherein the 
 delaying further comprises delaying until the measured dynamic pressure is lower than the first initial elevated pressure. 
 
     
     
       12. The method of  claim 11  wherein the delaying further comprises delaying until the measured dynamic pressure is about the initial hydrostatic pressure. 
     
     
       13. The method of  claim 1  wherein after opening the at least one of the one or more surge canisters the method further comprises opening at least a subsequent surge canister for sustaining the period of dynamic underbalance. 
     
     
       14. The method of  claim 1  wherein the delaying further comprises delaying until the burning of the propellant is substantially complete. 
     
     
       15. The method of  claim 1  wherein the period of dynamic underbalance is further maximized comprising actuating a pressure wave attenuator for isolating the zone of interest from hydrostatic pressure thereabove when the interface reflection pressure wave reaches the zone of interest. 
     
     
       16. The method of  claim 15 , wherein actuating the pressure wave attenuator is by a pressure differential found in the annulus when the interface reflection pressure wave reaches the zone of interest. 
     
     
       17. A method for creating a period of dynamic underbalance at a zone of interest in a wellbore comprising:
 positioning a perforation assembly in the wellbore at the zone of interest for creating an annulus between the assembly and the wellbore, the annulus containing fluid and having an initial hydrostatic pressure, the assembly having at least a propellant-type perforation gun and one or more surge canisters, the initial hydrostatic pressure encouraging maximal burn of propellant of the propellant-type perforation gun; 
 actuating the propellant-type perforating gun for igniting the propellant, creating an initial pressure event and forming perforations at the zone of interest and wherein dynamic pressure in the annulus at the zone of interest reaches a first initial elevated pressure; 
 delaying until the dynamic pressure diminishes from the first initial elevated pressure; 
 wherein the initial pressure event creates an interface reflection pressure wave traveling along the wellbore and wherein the delaying further comprises delaying until about the time the interface reflection pressure wave reaches the zone of interest; and then 
 opening at least one of the one or more surge canisters so as to receive a surge of the fluid therein for creating the period of dynamic underbalance, wherein the period of dynamic underbalance is further maximized comprising actuating a pressure wave attenuator for isolating the zone of interest from hydrostatic pressure thereabove when the interface reflection pressure wave reaches the zone of interest. 
 
     
     
       18. The method of  claim 17 , wherein actuating the pressure wave attenuator is by a pressure differential found in the annulus when the interface reflection pressure wave reaches the zone of interest.